A face lift for Federal Hill

Once again, engineers are trying to save the city landmark. Here's how the $1.9 million project is supposed to keep it from sliding into the harbor.

March 26, 2000|By Edward Gunts | Edward Gunts,Sun Architecture Critic

Like an old building with a sagging foundation, Baltimore's Federal Hill had structural problems that left it in danger of collapsing.

So for the past nine months, contractors have been rebuilding portions of it to improve drainage and make it more sound.

The $1.9 million preservation project was launched to address erosion problems dating from 1995, when a 90-foot fissure became visible on the north side of the hill. It's the third time in the past decade that the city has taken steps to stabilize the slope.

The work is comparable to the process of restoring a historic wood-frame house by removing sections of rotten wood and replacing them with sturdier materials. As with many examples of architectural restoration, the contractor's goal is to complete the work in such a way that most observers won't even know it's been done.

"It will look just like it did before, except that it won't have the erosion," said Kurt Kocher, spokesman for Baltimore's Department of Public Works.

Federal Hill takes its name from a party Baltimoreans threw in 1788 to celebrate Maryland's ratification of the Federal Constitution. There have been attempts to destroy the hill, including a proposal to level it and use the debris to fill the Inner Harbor, and a 1960s-era proposal to build a highway connecting it with Fells Point. But neither plan moved ahead, and it remains one of Baltimore's most popular gathering spots, with sweeping views of the downtown skyline and Inner Harbor.

Seven stories above sea level at its highest point, the hill has a history of instability that is related to its composition -- a mixture of sand, clay, silt and topsoil -- and previous uses.

In 1608, when Capt. John Smith became one of the first English explorers to see the hill, he described it in his journal as "a great red bank of clay flanking a natural harbour basin," according to local historian Norman Rukert's book, "Federal Hill."

Many alterations over the years

Early drawings indicate that it was much more of a cliff than it is today. Historians say the hill is honeycombed with tunnels that date to Colonial times, when its clay and sand were mined by glass manufacturers and brickmakers. During the Civil War, it was occupied by Union soldiers, who dug field fortifications that reshaped the top of the hill. In the late 19th century, it became a public park.

In 1992, the city spent $1.2 million on drainage control and stabilization work to correct erosion problems evident from the 1970s. Work done at the time included the installation of "underdrains" and repairing the retaining wall along Key Highway. Three years later, crews returned to complete drain repair and erosion control work totaling $550,000 as part of a park face lift.

When the 90-foot fissure appeared, even before the 1995 repairs were complete, city officials began another effort to save Federal Hill.

"This is where people came to celebrate the adoption of the Constitution," Kocher said. "It's a focal point for the neighborhood. It's a vantage point for the whole city."

After a thorough investigation, city engineers concluded that the earlier work was done in keeping with original specifications, but the scope of work wasn't extensive enough to halt the erosion. "It was a subsurface problem," Kocher said. "The previous work did not remove all of the bad soil."

The tunnels weren't considered part of the problem because they are farther south than the areas that were eroding.

This time, he said, a different consulting team called for a more thorough reconstruction of the hill, combined with installing a more elaborate underground drainage system.

The new plan for stability

The plan called for scraping eight feet of soil off the unstable areas -- the entire north slope and portions of the east and west slopes. The idea was to go down far enough to remove all soil that was shifting because it was sandy and claylike.

Then contractors dug trenches for new perforated pipes, 12 inches in diameter, to channel water from the hill to the city's storm drains. They also replaced the eight feet of sandy soil with seven feet of stones -- 3/4 inch to 1 1/2 inches in diameter -- covered by one foot of topsoil, recycled from what was near the top of the hill before.

Between the rocks and the topsoil is a layer of synthetic netting, called a Geoweb System, which holds the rocks and soil in place. The hill is being sown with a mixture of grasses designed to stabilize the hill (85 percent tall fescue, 10 percent perennial rye and 5 percent bluegrass) and covered with a woven fiber matting to promote seed germination.

Metal beams were installed at the northeast corner of the park to keep the hilltop from sliding down during reconstruction and will remain in place. Portions that stick out above the surface will be cut off at ground level. Contractors will reconstruct walkways at the top and midpoint of the hill, and reposition statues, cannons and other monuments along the northern edge, as they were before.

The engineers figure that the seven-foot layer of stones will be deep and porous enough to let water seep down and be carried from the hill through the perforated drain pipes.

Whitney, Bailey, Cox and Magnani of Towson studied the hill in 1998 and designed the stabilization plan. Pavex Inc. of Hunt Valley is the contractor. All work is scheduled to be completed by the end of April.

Kocher said city engineers and consultants are optimistic that this work will finally take care of the problem.

"The true test will come when it's all done and we see how things hold," he said.

But "the confidence level is very high. ... When you have a slope this steep, you have to take dramatic measures to stabilize it. We think this is the best technology available to fix the hill and still leave it in the configuration that people know."